It has been shown that cyclic nucleotides (cGMP, cAMP) mediate many of the normal functions of the neural retina, especially as related to the visual process. Moreover, protein kinases (cAMP- dependent protein kinase, C-kinase) mediate the function of these nucleotides as well as transduce other important signals (eg, calcium, lipids, etc.). We have evidence that (1) abnormalities in cAMP-dependent protein kinase may be involved in human retinoblastoma, (2) cyclic GMP accumulation and distribution is abnormal in photoreceptor cells of an animal model of inherited retinal degeneration and (3) C-kinase could be involved in normal light/dark mechanisms in the photoreceptor outer segment.